Conduit construction



July 9, 1957 J. H. MARTIN ET AL 2,798,510

CONDUIT CONSTRUCTION Filed July 18, 1955 JOHN ATTORNEYJ' United StatesPatent coNDUIT CONSTRUCTION John H. Martin and Edward s. Reid,Hartsville, s. c., assignors to Sonoco Products Company, a corporationof South Carolina Application July 18, 1955, Serial No. 522,678

3 Claims. (Cl. 138--78) This invention relates to conduit construction,and more particularly to paper conduit construction with exceptionalheat insulating properties.

The paper conduit constructed according to the present invention isadapted especially for use in conveying a fluid medium at varioustemperatures, such as a precooled air medium in an air conditioningsystem. In such a system the fluid medium is usually conveyed throughducts for quite a distance and it is, therefore important that thetemperature of the fluid medium is not adversely affected by thesurrounding atmospheric air conditions until this fluid medium hasreached the area to be conditioned thereby. It will be apparent that thepaper conduit described in detail below may also be used for otherpurposes besides air conditioning and in which good heat insulatingproperties are required. 1

In accordance with the present invention a conduit is constructed fromconcentric paper tubes having thermal insulating material such as forexample, glass fiber, mineral wool or the like, arranged between thetubes to provide a conduit of light weight, and of substantial strengthand stiffness, for conveying a fluid medium and protecting it fromadverse effects by the surrounding atmospheric air conditions.

The present invention is described in further detail below in connectionwith the accompanying drawings in which:

Fig. 1 is an elevation of a short length of conduit constructed inaccordance with the present invention;

Fig. 2 is a fragmentary sectional detail taken generally at 22 in Fig.1;

Fig. 3 is an elevation, partly in section, of the conduit shown in Fig.1;

Fig. 4 is a fragmentary sectional detail similar to Fig. 2 but showing amodified embodiment of the conduit construction of the presentinvention; and

Fig. 5 is a further fragmentary sectional detail similar to Fig. 2 butshowing a still further modified embodiment of the conduit constructionof the present invention.

Referring now to the drawings, the illustrated embodiment of the presentinvention comprises a conduit indicated generally by the referencenumeral 10, which is formed of two concentric tubular bodies 12 and 14and a layer of insulating material 16, such as glass fiber, mineral woolor the like, sandwiched between the tubular bodies. The inner tubularbody 12 of the conduit is preferably formed by spirally winding aplurality of paper strips in conventional superimposed relationship toform a laminated or multi-ply paperboard tube of desired length andthickness. The spirally wound paper strips are bonded together by meansof a suitable adhesive interposed between them as they are wound, sothat the result ing multi-ply tube wall is of sufficient thickness toprovide the proper strength and stiffness necessary for the conduit 10.

In addition, the inner tubular body 12 of the conduit 10 is preferablyprovided with a liner 18 of aluminum or other metal foil bonded to oneface of the body 12. This metal foil liner prevents contact withtheinner wall of the paperboard tubular body 12, of any condensation ofthe moisture content of the fluid medium being conveyed through theconduit 10. The metal foil also has the desirable properties of flameretarding, heat reflecting and low frictional losses to air flow.

Preferably, the aluminum of other metal foil in the form of a strip maybe bonded to the surface of the paper strip that forms the inner spiralwinding of the tubular body 12, so that the liner 18 is automaticallyformed thereon as the paper strips are wound to form the tubular body12.

Next, the application of the layer of insulating material 16 between thetubular bodies 12 and 14 of the conduit 10 may be carried outconveniently by spirally winding a strip of such insulating material onthe outer wall face of the tubular body 12 so as to form a layer ofsuflicient thickness to provide the proper insulation desired.Furthermore, the strip of insulating material forming the layer 16 maybe bonded to the outer wall face of the tubular body 12 by means of asuitable adhesive interposed therebetween as the insulation is wound onthe outer face of the tubular body 12.

This insulating material, however, may be obtained commercially in theform of a sheet made of two paper plies and a layer of insulatingmaterial bonded between them, which sheet of insulating material may becut into strips in order to be spirally wound on the tube 12 as shown inFig. 3.

Following the application of the layer 16 on the tubular body 12, theouter tubular body 14 is formed by employing a two-ply paper sheet 20,such as kraft paper, having a layer of asphalt between the plies. Thispaper sheet 20 may be cut into strips which are spirally wound on theinsulation layer 16 and bonded thereto bya suitable adhesive interposedtherebetween.

The two-ply paper with asphalt therebetween functions as a vapor barrierfor preventing moisture in the surrounding atmosphere from penetratingthe insulation layer and damaging its insulating properties.

Alternatively, this outer tubular body 14 may be a spirally wound papertube 22, as shown in Fig. 4, the same as the tubular body 12, and may bebonded to the insulation layer 16 in the same manner as before.

In a further modified form as shown in Fig. 5, the outer tubular body 14may be a spirally wound double corrugated paperboard strip 24, whichprovides additional insulation by the dead air spaces or air cells 26formed by the corrugations between their facing sheets 28, and may bebonded to the insulation layer 16 and to a twoply paper sheet 20 withasphalt in between.

The conduit 10 constructed in accordance with the present invention maybe formed in any desired length and may be cut into shorter lengths byconventional means, such as a saw, without affecting its properties.

The present invention has been described above for purposes ofillustration only, and is not intended to be limited by this descriptionexcept as defined in the appended claims.

We claim:

1. A conduit for conveying a fluid medium at various temperaturescomprising an inner, spirally wound paper tubular body, a spirally woundliner of metal foil on the inner face of said tubular body providing asmooth interior surface and preventing condensate from coming intocontact with said tubular body, a layer of glass fiber insulatingmaterial spirally wound on the outer face of said inner tubular body andbonded thereon, and an outer paper tubular body surrounding said layerof insulating material and bonded thereto, whereby the temperature ofthe fluid medium conveyed through said conduit is protected fromsurrounding atmospheric conditions.

2. A conduit constructed according to claim 1 and further characterized,in that said outer paper tubular body isrformed of a tvyo;p1y,paper;shet having a.laye.r of asphalt; in between.

3. A conduit constructed according ;to claim, 1 and furthercharacterized in :that ,said outer :paper tubular body is formed of adouble corrugated paperboard and of a twp-ply paper with asphalttherebetwcen.

References Cited in the file of this patent UNITED STATES PATENTS KellerAug. 29, Seigle Nov. 23, Magill Sept. 20, Hatch May 23, Hlavaty Nov. 10,Douglas Aug. 8, Marc Jan. 13 Stuart et a1. June 3,

FOREIGN PATENTS France May 31,

